Do note that the United States has a significant portion of its citizens who deny that human actions have anything to do with climate change mostly calling it a "liberal hoax" and other such terms. So simply acknowledging the fact that global warming is happening is a big thing in itself. Not everyone however is seeing the campaign positively from a media angle and the way the website is presented does not help much with a hashtag like #itsnotwarming unfortunately a lot of people won't understand that the rest of the message is that "it's dying" and might stop there in their interpetation of the campaign which could seriously backfire.
Actually, technically and scientifically the slogan is misleading - earth will be fine, it's the species on it that will disappear.